1. Field of the Disclosure
The instant disclosure relates to a frequency tracking circuit; in particular, to a frequency tracking circuit proceeding differentiation through a phase difference.
2. Description of Related Art
Regarding wired communications research in recent years, due to a growing demand of users on a network bandwidth, and fiber has advantages of a high bandwidth, a low loss, confidentiality, a long life, and is not subject to electromagnetic interference, and thus after years of industry positioning dialectic and discussion of technical specifications, and related application products market is gradually booming, Ethernet optical fiber network system has become one of crucial medium for broadband communications.
A clock and data recovery (CDR) circuit is an integral part of the Ethernet optical fiber network system, and the CDR is at a receiving end of a receiver, responsible for an appropriate processing of data received, and a main function of the CDR is to remove a noise from the data received and to generate a clock signal synchronous to the data for a next circuit to proceed a digital signal processing. The CDR is divided into two parts: a phase tracking circuit and frequency tracking circuit, to respectively proceed a phase and a frequency correction on the data received according to the clock signal provided by the CDR itself.
However, a frequency tracking circuit in prior arts requires two sets of clock signals with a phase difference of 90 degrees in between to detect a frequency difference, therefore, a design of an oscillator appears to be complicated and results in a waste of circuit area and power consumption. Furthermore, when the frequency tracking circuit in prior art proceeds a frequency tracking, it may interfere with a phase tracking so that an operation of the circuit appears unstable.